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gencls - class interface compiler for Prima core modules |
gencls - class interface compiler for Prima core modules
gencls --h --inc --tml -O -I<name> --depend --sayparent filename.cls
Creates headers with C macros and structures for Prima core module object definitions.
gencls accepts the following arguments:
-O
flag on, a thunk body is replaced to a call to
a function, which name is made up from all method parameters plus result.
Actual function is not written in .inc file, but in .tml file.
All duplicate declarations from a set of .tml files can be removed
and the reminder written to one file by tmlink utility.
-O automatically on.
In short, the syntax of a .cls file can be described by the following scheme:
[ zero or more type declarations ] [ zero or one class declaration ]
Gencls produces .h, .inc or .tml files, with a base name of the .cls file, if no object or package name given, or with a name of the object or the package otherwise.
Gencls has several built-in scalar data types, that it knows how to deal with. To 'deal' means that it can generate a code that transfers data of these types between C and perl, using XS ( see the perlguts manpage ) library interface.
The types are:
int Bool Handle double SV* HV* char * string ( C declaration is char[256] )
There are also some derived built-in types, which are
long short char Color U8
that are mapped to int. The data undergo no conversion to int in transfer
process, but it is stored instead to perl scalar using newSViv() function,
which, in turn, may lose bits or a sign.
The syntax for a new data types definition is as follows:
<scope> <prefix> <id> <definition>
A scope can be one of two pragmas, global or local.
They hint the usage of a new data type, whether the type
will be used only for one or more objects. Usage of
local is somewhat resembles C pragma static.
Currently the only difference is that a function
using a complex local type in the parameter list or
as the result is not a subject for -O optimization.
New scalar types may only be aliased to the existing ones, primarily for C coding convenience. A scalar type can be defined in two ways:
<scope> $id => <basic_scalar_type>;
Example:
global $Handle => int;
The new type id will not be visible in C files, but the type will be substituted over all .cls files that include this definition.
<scope> id1 id2
Example:
global API_HANDLE UV
Such code creates a C macro definition in .h header file in form
#define id1 id2
C macros with parameters are not allowed. id1 and id2 are not required to be present in .cls name space, and no substitution during .cls file processing is made. This pragma usage is very limited.
Complex data types can be arrays, structs and hashes. They can be a combination or a vector of scalar ( but not complex) data types.
Gencls allows several combinations of complex data types that C language does not recognize. These will be described below.
Complex data types do not get imported into perl code. A perl programmer must conform to the data type used when passing parameters to a function.
<scope> @id <basic_scalar_type>[dimension];
Example:
global @FillPattern U8[8];
Example of functions using arrays:
Array * func( Array a1, Array * a2);
Perl code:
@ret = func( @array1, @array2);
Note that array references are not used, and the number of items in all array parameters must be exactly as the dimensions of the arrays.
Note: the following declaration will not compile with C compiler, as C cannot return arrays. However it is not treated as an error by gencls:
Array func();
<scope> @id {
<basic_scalar_type> <id>;
...
<basic_scalar_type> <id>;
};
Example:
global @Struc {
int number;
string id;
}
Example of functions using structs:
Struc * func1( Struc a1, Struc * a2); Struc func2( Struc a1, Struc * a2);
Perl code:
@ret = func1( @struc1, @struc2); @ret = func2( @struc1, @struc2);
Note that array references are not used, and both number and order of items in all array parameters must be set exactly as dimensions and order of the structs. Struct field names are not used in perl code as well.
<scope> %id {
<basic_scalar_type> <id>;
...
<basic_scalar_type> <id>;
};
Example:
global %Hash {
int number;
string id;
}
Example of functions using hashes:
Hash * func1( Hash a1, Hash * a2); Hash func2( Hash a1, Hash * a2);
Perl code:
%ret = %{func1( \%hash1, \%hash2)};
%ret = %{func2( \%hash1, \%hash2)};
Note that only hash references are used and returned. When a hash is passed from perl code it might have some or all fields unset. The C structure is filled and passed to a C function, and the fields that were unset are assigned to a corresponding C_TYPE_UNDEF value, where TYPE is one of NUMERIC, STRING and POINTER literals.
Back conversion does not count on these values and always returns all hash keys with a corresponding pair.
Syntax:
<namespace> <ID> {
<declaration>
...
<declaration>
}
A .cls file can have zero or one namespace sections,
filled with function descriptions. Functions described here
will be exported to the given ID during initialization
code. A namespace can be either object or package.
The package namespace syntax allows only declaration
of functions inside a package block.
package <Package ID> {
<function description>
...
}
The object namespace syntax includes variables and properties as well as functions ( called methods in the object syntax ). The general object namespace syntax is
object <Class ID> [(Parent class ID)] {
<variables>
<methods>
<properties>
}
Within an object namespace the inheritance syntax can be used:
object <Class ID> ( <Parent class ID>) { ... }
or a bare root object description ( with no ancestor )
object <Class ID> { ... }
for the object class declaration.
Syntax:
[<prefix>] <type> <function_name> (<parameter list>) [ => <alias>];
Examples:
int package_func1( int a, int b = 1) => c_func_2;
Point package_func2( Struc * x, ...);
method void object_func3( HV * profile);
A prefix is used with object functions ( methods ) only. More on the prefix in the Methods manpage section.
A function can return nothing ( void ), a scalar ( int, string, etc ) or a complex ( array, hash ) type. It can as well accept scalar and complex parameters, with type conversion that corresponds to the rules described above in Basic scalar data types section.
If a function has parameters and/or result of a type that
cannot be converted automatically between C and perl,
it gets declared but not exposed to perl namespace.
The corresponding warning is issued.
It is not possible using gencls syntax to declare
a function with custom parameters or result data.
For such a purpose the explicit C declaration
of code along with newXS call must be made.
Example: ellipsis (...) cannot be converted by gencls, however it is a legal C construction.
Point package_func2( Struc * x, ...);
The function syntax has several convenience additions:
void func( int a = 15);
A function declared in such way can be called both with 0 or 1 parameters. If it is called with 0 parameters, an integer value of 15 will be automatically used. The syntax allows default parameters for types int, pointer and string and their scalar aliases.
Default parameters can be as many as possible, but
they have to be in the end of the function parameter list.
Declaration func( int a = 1, int b) is incorrect.
Example:
package Package {
void func( int x) => internal;
}
A function declared in that way will not
call Package_func() C function, but internal()
function instead. The only request is that internal()
function must have identical parameter and result declaration
to a func().
HV*, then parameter translation
from perl to C is performed as if all the parameters passed
were a hash. This hash is passed to a C function
and it's content returned then back to perl as a hash again.
The hash content can be modified inside the C function.
This declaration is used heavily in constructors, which perl code is typical
sub init
{
my %ret = shift-> SUPER::init( @_);
...
return %ret;
}
and C code is usually
void Obj_init ( HV * profile) {
inherited init( profile);
... [ modify profile content ] ...
}
Methods are functions called in a context of an object. Virtually all methods need to have an access to an object they are dealing with. Prima objects are visible in C as Handle data type. Such Handle is actually a pointer to an object instance, which in turn contains a pointer to the object virtual methods table ( VMT ). To facilitate an OO-like syntax, this Handle parameter is almost never mentioned in all methods of an object description in a cls file, although being implicit counted, so every cls method declaration
method void a( int x)
for an object class Object is reflected in C as
void Object_a( Handle self, int x)
function declaration. Contrary to package functions, that gencls is unable to publish if it is unable to deal with the unsupported on unconvertible parameters, there is a way to issue such a declaration with a method. The primary use for that is the method name gets reserved in the object's VMT.
Methods are accessible in C code by the direct name
dereferencing of a Handle self as a corresponding
structure:
((( PSampleObject) self)-> self)-> sample_method( self, ...);
A method can have one of six prefixes that govern C code generation:
method is therefore was chosen as the most
descriptive name. Methods are expected to be coded in C,
the object handle is implicit and is not included into a .cls description.
method void a()
results in
void Object_a( Handle self)
C declaration. A published method automatically converts its parameters and a result between C and perl.
public prefix is used. The methods declared with public
is expected to communicate with perl by means of XS ( see the perlxs manpage
) interface. It is also expected that a public method creates both
REDEFINED and FROMPERL functions ( see the Prima::internals manpage for
details). Examples are many throughout Prima source, and
will not be shown here. public methods usually have
void result and no parameters, but that does not matter much,
since gencls produces no conversion for such methods.
import prefix. This kind of a method can
be seen as method inside-out. import function does not
need a C counterpart, except the auto-generated code.
static prefix.
static methods are all alike method ones, except that
Handle self first parameter is not implicitly declared.
If a static method is called without an object ( but with
a class ), like
Class::Object-> static_method();
its first parameter is not a object but a ``Class::Object'' string. If a method never deals with an object, it is enough to use its declaration as
static a( char * className = "");
but is if does, a
static a( SV * class_or_object = nil);
declaration is needed. In latter case C code itself has to determine
what exactly has been passed, if ever. Note the default parameter
here: a static method is usually legible to call as
Class::Object::static_method();
where no parameters are passed to it. Without the default parameter such a call generates an 'insufficient parameters passed' runtime error.
weird prefix
denotes a method that combined properties both from static
and public. In other words, gencls generates no conversion
code and expects no Handle self as a first parameter for
such a method. As an example Prima::Image::load can be depicted,
which can be called using a wide spectrum of calling semantics
( see the Prima::image-load manpage for details).
c_only is a method that is present on a VMT
but is not accessible from perl. It can be overloaded from
C only. Moreover, it is allowed to register a perl function with a name
of a c_only method, and still these entities will be wholly
independent from each other - the overloading will not take place.
NB: methods that have result and/or parameters data types that
can not be converted automatically, change their prefix to c_only.
Probably this is the wrong behavior, and such condition have to signal
an error.
Prima toolkit introduces an entity named property,
that is expected to replace method pairs whose function
is to acquire and assign some internal object variable,
for example, an object name, color etc. Instead of
having pair of methods like Object::set_color and Object::get_color,
a property Object::color is devised. A property is
a method with the special considerations, in particular,
when it is called without parameters, a 'get' mode
is implied. In contrary, if it is called with one parameter,
a 'set' mode is triggered. Note that on both 'set' and 'get'
invocations Handle self first implicit parameter is
always present.
Properties can operate with different, but fixed amount
of parameters, and perform a 'set' and 'get' functions
only for one. By default the only parameter is the implicit
Handle self:
property char * name
has C counterpart
char * Object_name( Handle self, Bool set, char * name)
Depending on a mode, Bool set is either true or false.
In 'set' mode a C code result is discarded, in 'get' mode
the parameter value is undefined.
The syntax for multi-parameter property is
property long pixel( int x, int y);
and C code
long Object_pixel( Handle self, Bool set, int x, int y, long pixel)
Note that in the multi-parameter case the parameters declared after property name are always initialized, in both 'set' and 'get' modes.
Every object is characterized by its unique internal state. Gencls syntax allows a variable declaration, for variables that are allocated for every object instance. Although data type validation is not performed for variables, and their declarations just get copied 'as is', complex C declarations involving array, struct and function pointers are not recognized. As a workaround, pointers to typedef'd entities are used. Example:
object SampleObject {
int x;
List list;
struct { int x } s; # illegal declaration
}
Variables are accessible in C code by direct name
dereferencing of a Handle self as a corresponding
structure:
(( PSampleObject) self)-> x;
Dmitry Karasik, <dmitry@karasik.eu.org>. Anton Berezin, <tobez@tobez.org>.
the Prima::internals manpage, tmlink
This program is distributed under the BSD License.
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gencls - class interface compiler for Prima core modules |